This invention relates to electric lamps and, in particular, to an improved lead wire for electric lamps.
In the prior art, copper or various copper alloys have been used as the material for lead wire in electric lamps. A recurring problem has been the weakening or annealing of the copper during glass forming operations. As a specific example, in making incandescent lamps, the lead wires and exhaust tube are inserted into a flare and the smaller end of the flare is heated and pressed to make what is known as the stem.
The stem press operation softens the lead wires to the point that tie wires are used to assure lamp reliability, particularly against shock. The button forming and tie wire operations add steps to the manufacture of lamps, increasing cost and adding possible source of shrinkage (rejected lamps).
While a variety of materials have been tried as substitutes for the copper or copper-alloy lead wires, none had been found suitable. Metals or alloys that adequately withstand stem pressing at higher temperatures have too high a resistance, adversely affecting the efficacy of the lamp. While larger diameter wire might alleviate the problem somewhat, this solution causes other difficulties, such as increased cost and possible sealing problems.